If you bought it with YOUR money then yes its yours, take it back and if/when they find out you took it back you just tell them "look, this is my pipe, i bought it with my money and therefore you have no right to take it" If you bought it with your lunch money or something like that (where ur rents gave it to you) I would suggest you just sit one down (whichever one is more likely to understand the situation) and say something along the lines of "Alright look I realize you dont approve of pot and I will respect that, but by taking the pipe or destroying it you have done nothing other than waste money and I'll just have to spend more of it to buy a new one" This is almost exactly what I told my mother the first time I actually stood up for myself and it worked to my surprise.